Social groups are very dependent on the norms established by the group. Norms are the unspoken rules that govern a society. Each individual set of people who come together as a group have their own established norms relative to the group's needs.
For example: A family is a group within a larger society. In a family two different individuals marry and bring together the norms they were raised with and those that they change to meet their needs. After the two adjust to one another and begin to raise children the norms will become established as to the expectations of their child's behavior, their morals, and the way in which the family does things. One group of family members may adhere to strict bedtimes at eight at night while another group may decide that no specific bedtime is their peference. One group may allow their small child to sleep in their bed while the other may not.
Another example of a group are gangs. If a personis influenced by the camaraderie in a gang and feels a need to belong, he or she may become a member. Gangs have specific rituals for becoming a member, have their own rules, establish who can and can not be a member, and also have their own code of ethics. They establish mores that meet their needs and the needs of their members.